local($^W) does not work correctly

[p5pRT]

Migrated from rt.perl.org#16235 (status was 'open')

Searchable as RT16235$

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From jima@simplex.com

Created by jima@simplex.com

# local() doesn't seem to work correctly with $^W in Perl 5.6.1
# Run this program to see.
# -Jim Avera  jima@​simplex.com    8/15/2002

use strict;

#------ this works ------
use vars '$XX';
$XX = 1;
die "BUG​: XX is off" unless $XX;
{ local($XX) = $XX;
  die "BUG​: XX is off" unless $XX;
}
die "BUG​: XX is off" unless $XX;

#------ this doesn't work ------
$^W = 1;
die "BUG​: warn is off" unless $^W;
{ local($^W) = $^W;
  die "BUG​: warn is off" unless $^W;  # dies here in Win32 Perl 5.6.1 
}
die "BUG​: warn is off" unless $^W;    # dies here in Solaris Perl 5.6.1 

print "Test passed.\n";

Perl Info

``` Flags: category=core severity=medium Site configuration information for perl v5.6.1: Configured by carl at Tue Dec 11 12:21:24 PST 2001. Summary of my perl5 (revision 5.0 version 6 subversion 1) configuration: Platform: osname=solaris, osvers=2.7, archname=sun4-solaris uname='sunos bermuda 5.7 generic_106541-17 sun4u sparc sunw,ultra-5_10 ' config_args='' hint=recommended, useposix=true, d_sigaction=define usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef useperlio=undef d_sfio=undef uselargefiles=define usesocks=undef use64bitint=undef use64bitall=undef uselongdouble=undef Compiler: cc='/users/egcs/bin/gcc', ccflags ='-fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64', optimize='-O', cppflags='-fno-strict-aliasing -I/usr/local/include' ccversion='', gccversion='2.95.2 19991024 (release)', gccosandvers='solaris2.6' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=4321 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16 ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8 alignbytes=8, usemymalloc=y, prototype=define Linker and Libraries: ld='/users/egcs/bin/gcc', ldflags =' -L/usr/local/lib ' libpth=/usr/local/lib /usr/lib /usr/ccs/lib libs=-lsocket -lnsl -ldl -lm -lc perllibs=-lsocket -lnsl -ldl -lm -lc libc=, so=so, useshrplib=false, libperl=libperl.a Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' ' cccdlflags='-fPIC', lddlflags='-G -L/usr/local/lib' Locally applied patches: @INC for perl v5.6.1: /usr/local/lib/perl5/5.6.1/sun4-solaris /usr/local/lib/perl5/5.6.1 /usr/local/lib/perl5/site_perl/5.6.1/sun4-solaris /usr/local/lib/perl5/site_perl/5.6.1 /usr/local/lib/perl5/site_perl . Environment for perl v5.6.1: HOME=/hcusers/jima LANG (unset) LANGUAGE (unset) LD_LIBRARY_PATH (unset) LOGDIR (unset) PATH=/usr/local/bin:/usr/local/gcc/3.1/bin:/usr/local/gcc/gdb-5.2/bin:/usr/bin:bin/sun5:libdft/src:../../bin/sun5:../../libdft/src:/hcusers/jima/work/output/sun5/bin:/hcusers/jima/work/libdft/src:/hcusers/jima/work.mess/output/sun5/bin:/hcusers/jima/work.mess/libdft/src:/hcusers/jima/bin/sun5:/hcusers/jima/bin:/hcusers/jima/jima_tools/bin:/bin:/opt/SUNWspro/bin:/users/egcs/2.95.3/bin:/users/egcs/bin:/users/gnu/bin:/usr/5bin:/usr/X/bin:/usr/ccs/bin:/usr/openwin/bin:/usr/sbin:/usr/ucb:/usr/xpg4/bin:. PERL_BADLANG (unset) SHELL=/usr/bin/bash ```

[p5pRT]

From @schwern

Confirmed in 5.8.0 and 5.8.1 RC2.

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@schwern - Status changed from 'new' to 'open'

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From @Hugmeir

On Tue Jul 15 23​:16​:04 2003\, schwern wrote​:

Confirmed in 5.8.0 and 5.8.1 RC2.

This is still present in 5.14.2 and blead\, but a small update​: The original bug report says that Solaris behaved differently\, failing on the final die. Now it's the same same place as Linux/Windows\, on

{ local($^W) = $^W; die "BUG​: warn is off5" unless $^W; }

[p5pRT]

From @cpansprout

On Sat Apr 28 02​:11​:01 2012\, Hugmeir wrote​:

On Tue Jul 15 23​:16​:04 2003\, schwern wrote​:

Confirmed in 5.8.0 and 5.8.1 RC2.

This is still present in 5.14.2 and blead\, but a small update​: The original bug report says that Solaris behaved differently\,

Knowing how this is implemented\, I think it was misdiagnosed.

failing on the final die. Now it's the same same place as Linux/Windows\, on

{ local($^W) = $^W; die "BUG​: warn is off5" unless $^W; }

Usually\, local($foo) creates a new $foo in *foo{SCALAR}\, copies the magic to it\, and then calls set-magic on it. This allows a plain local($^W); to work.

local($foo) = $foo works because the $foo on the RHS (which is executed first) is the original $foo; i.e.\, a completely different scalar.

For magical variables things gang agley\, because the local($^W) on the LHS is a separate operator from assignment and sets $^W to undef befor the assignment happens. Since both $^W’s have magic that writes to the same underlying structures\, the assignment has no affect.

This is similar to bug #104118\, but a little different; but I think it’s the same code that would need adjustment.

--

Father Chrysostomos

[p5pRT]

From @cpansprout

On Sat Apr 28 13​:56​:58 2012\, sprout wrote​:

On Sat Apr 28 02​:11​:01 2012\, Hugmeir wrote​:

On Tue Jul 15 23​:16​:04 2003\, schwern wrote​:

Confirmed in 5.8.0 and 5.8.1 RC2.

This is still present in 5.14.2 and blead\, but a small update​: The original bug report says that Solaris behaved differently\,

Knowing how this is implemented\, I think it was misdiagnosed.

failing on the final die. Now it's the same same place as Linux/Windows\, on

{ local($^W) = $^W; die "BUG​: warn is off5" unless $^W; }

Usually\, local($foo) creates a new $foo in *foo{SCALAR}\, copies the magic to it\, and then calls set-magic on it. This allows a plain local($^W); to work.

local($foo) = $foo works because the $foo on the RHS (which is executed first) is the original $foo; i.e.\, a completely different scalar.

For magical variables things gang agley\, because the local($^W) on the LHS is a separate operator from assignment and sets $^W to undef befor the assignment happens. Since both $^W’s have magic that writes to the same underlying structures\, the assignment has no affect.

I forgot to mention that local($hash{elem}) in lvalue context is special-cased to work\, for the sake of %SIG. There are various /* XXX - FIXME - see #60360 */ comments sprinkled here and there.

--

Father Chrysostomos

[p5pRT]

From @mauke

Created by @mauke

% perl -wle '$? = 123; print "before: $?"; local $? = $?; print "after: $?"'
before: 123
after: 0

% perl -wle '$? = 123; print "before: $?"; local $? = $? + 0; print "after: $?"'
before: 123
after: 123

I would have expected the first version to output "after: 123" instead of resetting $? to 0. Oh wait, it's actually worse than I thought:

% perl -wle '$? = 123; print "before: $?"; { local $? = $?; print "after: $?"; } print "finally: $?"'
before: 123
after: 0
finally: 0

i.e. the reset isn't even localized; it straight up clobbers $?.

This bug interacts badly with END blocks:

% perl -e 'exit 123; END { local $? = $?; }'; echo $?
0

instead of the expected:

% perl -e 'exit 123; END { local $? = $? + 0; }'; echo $?
123

Perl Info

``` Flags: category=core severity=low This perlbug was built using Perl 5.12.1 - Thu Jun 3 20:09:15 CEST 2010 It is being executed now by Perl 5.16.0 - Mon May 21 12:24:16 CEST 2012. Site configuration information for perl 5.16.0: Configured by mauke at Mon May 21 12:24:16 CEST 2012. Summary of my perl5 (revision 5 version 16 subversion 0) configuration: Platform: osname=linux, osvers=2.6.38-gentoo-r6, archname=i686-linux uname='linux nora 2.6.38-gentoo-r6 #1 preempt sat aug 6 03:05:34 cest 2011 i686 amd athlon(tm) 64 processor 3200+ authenticamd gnulinux ' config_args='-Dcc=cgcc -Dprefix=/home/mauke/usr/local -Dman1dir=none -Dman3dir=none -Dinc_version_list=none -Doptimize=-O2 -flto' hint=recommended, useposix=true, d_sigaction=define useithreads=undef, usemultiplicity=undef useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef use64bitint=undef, use64bitall=undef, uselongdouble=undef usemymalloc=n, bincompat5005=undef Compiler: cc='cgcc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64', optimize='-O2 -flto', cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include' ccversion='', gccversion='4.6.3', gccosandvers='' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12 ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8 alignbytes=4, prototype=define Linker and Libraries: ld='cgcc', ldflags ='-fstack-protector -L/usr/local/lib -O2 -flto' libpth=/usr/local/lib /lib/../lib /usr/lib/../lib /lib /usr/lib libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc libc=/lib/libc-2.14.1.so, so=so, useshrplib=false, libperl=libperl.a gnulibc_version='2.14.1' Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E' cccdlflags='-fPIC', lddlflags='-shared -O2 -flto -L/usr/local/lib -fstack-protector' Locally applied patches: SAVEARGV0 - disable magic open in @INC for perl 5.16.0: /home/mauke/usr/local/lib/perl5/site_perl/5.16.0/i686-linux /home/mauke/usr/local/lib/perl5/site_perl/5.16.0 /home/mauke/usr/local/lib/perl5/5.16.0/i686-linux /home/mauke/usr/local/lib/perl5/5.16.0 . Environment for perl 5.16.0: HOME=/home/mauke LANG=en_US.UTF-8 LANGUAGE (unset) LC_COLLATE=POSIX LD_LIBRARY_PATH=/home/mauke/usr/local/lib LOGDIR (unset) PATH=/home/mauke/usr/perlbrew/bin:/home/mauke/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.6.3:/opt/sun-jdk-1.4.2.13/bin:/opt/sun-jdk-1.4.2.13/jre/bin:/opt/sun-jdk-1.4.2.13/jre/javaws:/opt/dmd/bin:/usr/games/bin PERLBREW_BASHRC_VERSION=0.43 PERLBREW_HOME=/home/mauke/.perlbrew PERLBREW_PATH=/home/mauke/usr/perlbrew/bin PERLBREW_ROOT=/home/mauke/usr/perlbrew PERLBREW_VERSION=0.27 PERL_BADLANG (unset) PERL_UNICODE=SAL SHELL=/bin/bash ```

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From @ikegami

Also affects Windows and cygwin\, so it's not OS specific.

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The RT System itself - Status changed from 'new' to 'open'

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@ikegami - Status changed from 'open' to 'new'